Mechanical hammer



'sept 25, 1945.

' c. H. GUBBINS MECHANICAL HAMMER Filed March 14, 1944 2 Sheets-Sheet 2 R.. OWN". .0N 0% fr d gm n mvww www C1 VY Inventor CHARLES Remb( Guinl,

Spt. 2 5, 1945; c.` H. GuBBlNs 2,385,439

l MECHANICAL HAMMER Filed March 14, 1944 2 sheets-sheet 1 A ltorney Patented Sept. 25, 1945 S PATENT OFFICE Y MECHANICAL HAMMER Charles Henry Gubbins, Ealing, London, England 'Application March 14, 1944, Serial No. 526,463

Y I In Great Britain August 27, 1943 4 Claims.

The invention relates to tools of the kind in which hammer blows are applied by mechanical means to a drill, chisel, riveting snap, punch or other implement (hereinafter referred to as a bit) carried in a holder forming part of the tool.

Tools of this kind las hitherto known suffer from the drawback that, so longas power is supplied to the tool, the application of hammer blows to the bit continues irrespective of Whether or not the bit is in engagement with the work. As the application of theuhammer blowson the bit when the latter is in contact with the work, already imposes a considerable strain on the parts, resulting in wear, one can well appreciate that the working life of the tool is further reduced by reason of the fact lthat these blows continue while the bit is performing no useful work. This objection would be overcome if the power supply were cut off at the instant the bit is lifted from the work, but that would, in some cases, depend upon the skill of the individual workman in manipulating the tool, while, in other. cases, the nature of the power supplied is such that it cannot readily be cut off by the person handling the tool.

The object of the present invention is to provide a construction of tool of the kind in question in which the objections referred to are erradicated, the construction being such that hammer blows cannot in any case be applied to the bit unless the latter is pressed against the work. Stated in another way, the construction is such that the hammer blows applied to the bit cease as soon as the latter is lifted from the work, and this without interrupting the supply of power to the tool.

According to the invention hammer blows are applied directly or indirectly to the bit by means of a moving slug or block adapted to be influenced by a mechanically driven reciprocating member, means being provided whereby the said reciprocating member has no influence upon the slug or block unless and until the bit is Dressed against the work.

More specicallyin a tool according to the invention the bit holder is movable and hammer l blows thereon are imposed by a slug or block displacement by the act of pressing the bit against the work.

Any suitable means may be employed for propelling the reciprocating member, it may be driven by hand through the medium of a crank or the like or by power such as that obtained from an electric motor.

In order that the invention may be more readily understood, reference is now made to the accompanying drawings which illustrate one ernbodiment given by way of example and in which driving power is supplied by an electricrmotor forming part of the tool. In the drawings:

Figure 1 is a longitudinal section through the complete tool, this figure showing the reciprocating member at its forward dead-centre position, and also indicating the position assumed by bit holder and slug when they are in a state of rest, namely, before the slug has received a preliminary displacement.

Figure 2 is a side'elevation of the tool.

Figure 3 is a sectional view corresponding to the left-hand end of Figure l, but showing the position assumed by the bit holder and slug when the latter has received a preliminary displacement under the effect of pressure of the bit on the work,

Figure 4 is a view corresponding to Figure 3, but showing the slug engaged by the reciprocating member with the latter closely approaching its rearward dead-centre position.

The electric motor by which the tool illustrated is driven, and which is generally indicated at i, is mounted in a housing 2 to the rear end of which is secured a hand grip 3. Current to the motor is supplied by a flexible connection 4 supported from the hand grip and the latter has a trigger switch 5 for closing and opening the circuits when desired.

The rear end of the shaft G of the rotor I of the motor I is journalled in a ball bearing 8 mounted in the hand grip 3, while the forward end of the shaft is journalled in a ball bearing 8 mounted in a plate IU which is secured to the forward end of the motor housing 2. This plate has slots I I through which air is ejected by means of a fan I2 on the motor shaft for cooling the motor.

To the plate I0 is secured a gear box I 3 containing a lay shaft I3 which is rotatable in two ball bearings I4, one mounted in the plate Iii and the other in the forward end of the gear box, the lay shaft being driven from the rotor shaft through reduction gearing generally indicated at I5.

The lay shaft is provided with a swash plate I6 upon which is journalled a connecting rod l 1, the arrangement being such that, on the shaft being rotated and the connecting rod being restrained against rotation, the free end I8 of the latter will execute a rocking movement under the influence of the swash plate. The free end of the connecting rod engages in a slot I9 in the rear end of a reciprocating member which `can conveniently be referred to as a piston rod. This rod is journalled in a bearing block 2l `which is carried by the forward end of the gear box I2 and has screw-threaded engagement with the rear end of a forwardly extending barrel 22, the block thereby serving to hold the barrel securely in position against the gear box.

The forward end of the barrel ,22 carries the bit holder generally indicated at 23. The bit holder is in two parts, that is to say, it consists of a carrier 24 in the form of a sleeve which receives the bit holder proper 25. The carrier` is slidable in a bearing bush 25 in the barrel 22 and at its inner end has a ange 21 adapted to bear against a shoulder 28 ywithin the barrel so as t0 limit the forward travel of the carrier and l prevent its ejection from vthe barrel. The rearward travel of the carrier under pressure from the bit 29 when the latter is pressed against the work 39 (see Figures 3 and 4) is limited by a stop ring 3| secured to the carrier. is normally maintained in its forward position, with the ange 21 thereof in engagement with the shoulder 28, by means of a coil spring 32 which surrounds the forward end of the barrel,

the rearward end 33 of the spring being anchored f in a groove in the surface of the barrel and the forward end 34 being anchored in a groove in the surface of the bit holder 25 proper. The forward end of the spring has an eye 35 (Figure 2) to enable this end to be twisted and thereby expanded, thereby facilitating engagement of the bit holder withthe spring during .assembly or its disengagement during dismantling.

Within the barrel 22, there kis slidably mounted a slug 36 which is adapted to apply hammer blows to the carrier 24 and which is urged towards the carrier 24 by means of a compression spring 37 acting between the slug and the bearing block 2 l. In the normal position of the parts indicated in Figure 1, the bit holder 23 is situated in its extreme forward position, under the effect of the spring 32 and the slug 36 lies up against a shoulder 38 within the barrel 22 under the effect of the spring 3l. In this position, there is a slight clearance between the striking surface of the slug and the adjacent anvil surface of the carrier 24 of the bit holder. The slug 36 has a bore 39 into which penetrates the forward end ofthe piston rod 29, this end being provided with a conical head 40 which precedes a reduced portion of the piston rod so as to provide a shoulder 4I.

The slug 36 has a transverse slot in which works a plunger 42 which has a perforation 43 receiving the head 40 of the piston rod 20 and which is urged downwardly by means of a spring 44 carried by the slug. 'I'he upper edge 45 ofthe perforation 43 is chamfered and lies in the path of the conical surface of the head 40 of the piston rod 20. The lower end 46 of the plunger is chamfered and co-operates with a cam plate 41 which may be formed integrally with the barrel l22, but which, in the embodiment illustrated, is constituted by a separate part laid against an opening in the barrel and held detachably in position by spring straps 48 which pass through holes in The carrier 1 the plate and engage in recesses around the barrel. This plate hasa longitudinal recess 49 accommodating the chamfered lower end 46 of the plunger 42 and terminating at its rear end in a ramp or upwardly extending cam surface 50. The plunger 42 acts as means for coupling the slug to the piston rod in the manner hereinafter described.

When the bit holder 23 and the slug 36 are in a position of rest as indicated in Figure 1, the plunger 42 has no driving connection with the piston rod 20 even when the latter is in its forward dead-centre position. Hence, under these conditions, even if the electri-c motor l be started, so causing the piston rod to be reciprocated through the driving connections in the gear box YI2, the slug will remain stationary and therefore will not execute any hammering movement To cause the slug to partake of hammering movements it is rst necessary to press the bit 29 against the work 39, this pressure causing a rearward displacement of thebit holderrelatively to the barrel 22 against the action of the spring 32 until the stop ring 3| cornes up against the end of the barrel 22. This displacement will cause a corresponding rearward displacement of the slug .relatively to the barrel .as indicated in Figure 8. Under these conditions, and assuming that the piston rod is in its forward dead-centre position, the chamfered upper edge. 4.5 of the perforation 43 .in the plunger 42 will ride up the conical surface of the head 40 ofthe piston rod, so displacing the plunger upwardly against the pressure of thespring 44, until the .plunger has passed to the rear `of the head, whereupon the plunger will snap backso that its front face will engage behind the shoulder 4| on the pistonrod. Should it be that the piston rod is not at its forward dead-centre position at the time the slug Yis displaced in the manner described, vthe engagement of the plunger 42 behind the head of the piston rod will take place as a matter of course when the piston rod moves to its forward deadcentre position.

With the plunger engaged behind the head of the piston rod, the slug will be coupled to the piston rod so that, on its passage towards the rearward .dead-centre position, the piston rod will carry the slug with it, thereby drawing .the slug away from the bit vholder 23 and causing the spring 31 to be compressed as indicated in Figure 4. Meanwhile, .it will be noted that, by reason of the pressure initially -imposed upon the bit 29, the flange 2'! on the carrier 24 of the bit holder will be situated away from the shoulder 28 in the barrel v22 so that the bit holder -will be free to move forwardly when struck by the slug.

As the piston rod, carrying the slug with it, approaches its rearward dead-centre position, the chamfered lower end 46 of the plunger 42 will ride up the ramp 50 'on the cam plate 4l, so raising the plunger against'the pressure ofthe spring 44 until the front face of theiplunger is disengaged from the shoulder 4l on the kpiston rod. The slug will thereby be uncoupled from the piston rod and the energy stored up in the spring 31 will react instantly -to drive the slug rapidly forward so that its striking surface will come linto contact with theanvil surface of the carrier 24, thereby delivering a hammer blow to the bit carrier. The ramp 5l] is so lpositioned that the slug is uncoupled from the piston `rod just before the latter reaches its rearward deadcentre position.

v.So long ,as the Abit `29 ismaintainedwith-requisite pressure against the Work 35) to keep the bit holder in its inner position, the slug, having delivered a hammer blow, will remain in a position from which it can be picked up by the piston rod and moved away from the bit holder until it is again released for delivering another hammer blow. However, as soon as the tool is moved away from the work, the bit holder will move forwardly relatively to the barrel 22 and so the slug, under the action of the spring 31, will be free to move forward until it reaches a position which is beyond the eiective range of 4the piston rod. Hence, no further hammer blows will be imposed, notwithstanding a continuance of the supply of power to the tool, in which event the piston rod will merely reciprocate idly.

It Will be seen that the construction according to the invention provides an eiective solution to the problem of causing a cessation of hammer blows to the bit except when the latter is positioned against the work and is ready for attack, even though there is a continuation of supply of driving power to the tool.

What I claim and desire to secure by'Letters Patent in the United States is:

l. In a power drill or the like comprising a movable percussion member, a reciprocating drive mechanism, a movable slug engageable with said percussion member means to urge the slug towards the percussion member and means controlled by movement of the slug by engagement of the percussion member with the work for connecting the slug to the drive mechanism and releasing it therefrom, said slug having a slot therein transverse to its direction of movement, a catch piece slidable in said slot, said piece having a surface at a small angle to the direction of movement of the slug, said drive mechanism including a reciprocating pin having a surface formed at substantially the same angle as the surface on said piece and engageable therewith and having a shoulder behind such surface, said piece being urged to move in said slot in a direction to cause engagement of sai-d surfaces when the pin is near the percussion member, and said shoulder being engageable below said catch piece when the slug is pushed upward by engagement of the percussion member with the work.

2. In a power drill or the like comprising a movable percussion member, a reciprocating drive mechanism, a movable slug engageable with said percussion member, means to urge the slug towards the percussion member, and means controlled by movement of the slug by engagement of the percussion member with the work for connecting theslug to the drive mechanism and releasing it therefrom, said slug having a central opening in its upper end extending in the direction of movement of the slug and a slot intersecting said opening and transverse to the direction oi movement of the slug, a catch piece slidable in said slot and having a hole therethrough in the direction of movement of the slug, said drive mechanism including a pin reciprocating in the direction of movement of the slug and aligned with the opening, said piece being urged to move in said slot in a direction to engage said pin, said piece and said pin having cooperating means thereon to connect the slug to the pin when the slug is moved inward by engagement of the percussion member with the work.

3. In a power drill or the like comprising a movable percussion member, a reciprocatingrdriveV mechanism, a movable slug engageable with said percussion member means to urge the slug towards the percussion member and means controlled by movement of the slug by engagement of the percussion member With the work for connecting the slug to the drive mechanism and releasing it therefrom, said slug having a central opening in its upper end extending in the direction of movement of the slug and a slot intersecting said opening and transverse to the direction of movement of the slug, a catch piece slidable in said slot and having a hole therethrough in the direction of movement of the slug, said drive mechanism including a pin reciprocating in the direction of movement of the slug and aligned with the opening, said piece having in said hole a surface at a small angle to the direction of movement of the slug, said pin having a surface formed at substantially the same angle as the surface on said piece and engageable therewith and having a shoulder behind such surface, said piece being urged to move in said slot in a direction to cause engagement of said surfaces when the pin is near the percussion member, and said shoulder being engageable below said catch piece when the slug is pushed upward by engagement of the percussion member with the work.

4. In a device as claimed in claim 3, means forming a cam surface in the path of said piece when the slug is moved away from the percussion member to move said piece to a position to release the pin whereby the slug moves to strike the percussion member.

CHARLES HENRY GUBBINS. 

